1. Field of the Invention
The present invention relates to an apparatus to close, stretch and nail the flanks of a shoe vamp of a respective insole, in particular in machines for assembling shoe parts of the type comprising: a bed; column means operatively mounted to the bed and arranged to rigidly support, in an overturned position, a shoe being worked and comprised of a vamp and an insole engaged on a respective shoe last; two nailing units operatively mounted to the bed at the opposite sides of the column means respectively and each designed to act along one flank of the shoe being worked in order to stretch the vamp towards the insole and fasten the vamp edge to the insole by driving in nails.
2. Prior Art
It is known that is shoe factories automatic machines are used that lend themselves to act along the flanks of a shoe being worked in order to carry out the fastening of the lower vamp edge to the shoe insole, by driving in nails according to a predetermined pitch. To this end these machines are generally comprised of two nailing units operatively mounted to the support bed and respectively located to the opposite sides of column means suitably supporting the shoe being worked in an overturned position, the shoe having been previously fitted on a respective shoe last. Each nailing unit is provided with a nailing hammer which is moved along the corresponding shoe flank following the perimetrical extension of the insole. During the translation, the hammer carries out the driving in of a plurality of nails distributed according to a predetermined pitch, so as to cause the fastening of the lower vamp edge to the insole.
In some recently conceived machines each nailing unit is provided to be associated with stretching members adapted to act on the vamp in front of the hammer in order to stretch the vamp towards the insole. The action of these stretching members aims at ensuring a perfect adjustment of the vamp to the last configuration causing the vamp material in excess to be brought onto the insole where it will be fastened by the next nailing operation.
The machines of the above type have shown problems as regards working speed, practicality in use and qualitative level of the obtained product.
In the connection it is to be noted that in all known machines the shoe being worked has a fixed positioning on the column means, whereas the nailing hammers are caused to move along the shoe itself either in the longitudinal direction or in height or in a transverse direction in order to follow the outline of the perimetrical flank extension as faithfully as possible. The longitudinal translation of hammers takes place upon command of actuators, whereas hammers are moved transversely and in height by means of cams, auxiliary actuators or other devices the operation of which must be adjusted each time depending upon the type of shoe being worked. As adjustments are required, the use of these machines needs the presence of qualified man-power.
In some cases the movement of hammers is provided to be controlled by electronic systems capable of driving the operation of said hammers along the perimetrical flank extension of a shoe in a precise manner. However these electronic systems too need adjustments and/or data to be input by highly qualified staff.
It has also been found that the vamp stretching operation before the hammers and therefore in areas that necessarily are located far away from the nail driving in point, is not an optimum solution for the achievement of a perfect work. The material forming the vamp can in fact exhibit undesired elastic shrinkages at the moment that the action of the stretching members ceases, after the nails have been driven in.